The present invention relates to the field of cathode ray tube manufacture. More particularly, the present invention relates to the process of coating the narrow neck portion of a cathode ray tube funnel with a carbon material. Specifically, the present invention provides an improved shaft on which a sponge is supported for coating carbon material in the narrow neck portion of a cathode ray tube funnel prior to the sealing of the tube.
Cathode ray tubes (xe2x80x9cCRTsxe2x80x9d) are used in most television sets and computer and video monitors. A typical CRT is illustrated in FIG. 1. The CRT (100) is a glass tube with a bottle-like shape in which a relatively flat bottom portion (101) is sealed to a funnel (102). The funnel narrows into an elongated neck portion (102n). The relatively flat portion (101) of the CRT (100) becomes the screen on which the display of the television set or monitor is generated when the CRT is incorporated therein. An electro-luminescent material, such as phosphorus, that emits light when struck by an electron beam, is coated over the interior of the screen portion (101) of the CRT (100).
An electron gun (105) is then installed in the neck (102n) of the CRT (100). A stream of electrons (1070 emitted from the electron gun (105) is scanned over the electro-luminescent layer and turned on and off during the scanning to cause the electro-luminescent layer to glow in certain places and not others. In very simple terms, this is how an image is generated on the screen of a television or video monitor.
A yoke (not shown) is provided around the neck (102) of the CRT (100). This yoke produces a changing magnetic field through which the electron beam (107) from the electron gun (105) passes. The electron beam (107) is deflected by the magnetic field of the yoke. Consequently, by varying the magnetic field created by the yoke in a precise cycle, the electron beam (107) can be scanned, line-byline, over the entire surface of the screen (110) to generate video images thereon.
A cathode ray tube is generally constructed in the following matter. The funnel portion (102) of the CRT (100) is formed open at both ends. Then the relatively flat display portion (101) is sealed to the large end of the funnel (102) and the electron gun (105) is installed in the narrow end or neck (102n) of the funnel.
The display portion (101) is sealed to the funnel (102) using frit. Frit is a glass paste that can be cured or hardened. Frit (103), in paste form, is applied around the large end of the funnel (102) between the funnel (102) and the display portion (101). The frit is then cured or hardened to form a frit seal (103) between the funnel (102) and the display portion (101).
Before the funnel (102) and display (101) portions are sealed, a coating is applied to the interior of the funnel (102). This coating includes carbon material necessary to the optimal operation of the CRT (100). FIG. 2 illustrates a portion of a CRT production line in which the carbon material coating is applied to the interior of the funnel (102).
As shown in FIG. 2, cathode ray tube funnels (102) are supported during processing on holders or pallets (200). The pallets (200) include a base (201) with supports (202) that hold the funnel (102) in an upright position with the open, large end of the funnel (102) pointing upward. The pallets (200) carrying the funnels (102) may be transported on a conveyor (203).
First, each funnel (102) is brought to the coating application station (205). At the coating application station (205), the coating of carbon material is sprayed into the interior of the funnel (102). A spray head (204) sprays the coating into the open interior of the funnel (102) as the funnel (102) is supported on the pallet (200). Then, the funnel (102) is conveyed into and through a drying oven (206) to dry the newly applied coating.
In addition to this spraying process to coat the interior of the funnel (102) with carbon material, the narrow neck portion (102n) of the funnel (102) must also be fully coated with carbon material. Because of the narrow aspect of the neck (102n) below the main funnel (102), the sprayer (204) cannot be assured of fully coating the interior of the neck (102n) with carbon material.
Consequently, to complete the coating of the neck (102n) of the funnel (102), a stainless steel shaft is used that supports a sponge which is saturated with the carbon coating. The shaft and sponge are pushed through the neck of the funnel to fully coat the neck with the carbon coating. The shaft is always made of stainless steel. Presently, such a shaft costs about $190.
Unfortunately, there are several problems with this present system. First of all, as shafts are installed and replaced, shafts are periodically misplaced. This is particularly costly and unacceptable due to the relatively high expense of each shaft.
Additionally, for each week the system is operated, several shafts will be damaged and rendered unusable. The stainless steel shafts are damaged when the funnel is not precisely aligned under the robot. When the shaft is then plunged into the funnel, if the funnel and its neck are not precisely aligned with the downward path of the shaft, the shaft will be bent by insertion into the misaligned funnel.
Once the stainless steel shaft is bent, it is generally rendered unusable. However, it may be some time before the damage to the shaft is noticed. During this time, any funnels that are processed, i.e., are coated with carbon coating using the sponge on the bent shaft, may have uneven coating applied in the interior of the necks of those funnels. This is because of the bend in the damaged shaft. Such uneven coating of the neck may readily result in a CRT that is of low quality and unreliable when that unevenly coated funnel is used to construct that CRT.
Additionally, once the damage to the shaft is discovered, there is a significant amount of downtime required to remove and replace the damaged shaft. This downtime obviously decreases the efficiency and output of the production line of cathode ray tubes.
Consequently, there is a need in the art for an improved method and system of applying carbon coating in the interior of the narrow neck of a cathode ray tube funnel. Preferably, such an improved method and system should not rely on expensive and easily damaged stainless steel shafts.
The present invention meets the above-described needs and others. Specifically, the present invention provides an improved method and system of applying carbon coating in the interior of the narrow neck of a cathode ray tube funnel. This improved system does not rely on expensive and easily damaged stainless steel shafts.
Additional advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The advantages of the invention may be achieved through the means recited in the attached claims.
The present invention may be embodied and described as a system for applying a carbon coating to an interior of a neck portion of a cathode ray tube funnel. The system preferably includes a shaft made of a flexible, non-metallic material; a sponge attached to the shaft for spreading the carbon coating; and a robot for moving the shaft and the sponge through the neck portion of a cathode ray tube funnel.
The sponge is saturated with the carbon coating. Tubing may be included in the shaft for supplying the carbon coating to the sponge. A pump may also be connected to the tubing for pumping the carbon coating from a supply of such carbon coating through the tubing to the sponge.
A conveyor system may be used for automatically aligning the cathode ray tube funnels under the robot and the shaft. If the conveyor system misaligns the funnels, the flexible, non-metallic shaft will not be damaged by insertion through the misaligned funnel.
The shaft preferably includes a base for securing the sponge to the shaft. The shaft is preferably made of a composite plastic material. Most preferably, the shaft is made of Garolite.
The present invention also encompasses the methods of making and using the system and shaft described above. Specifically, the present invention encompasss a method of applying a carbon coating to an interior of a neck portion of a cathode ray tube funnel by pushing a shaft made of a flexible, non-metallic material through the neck portion of a cathode ray tube funnel, a sponge being attached to the shaft for spreading the carbon coating on the interior of the neck portion of the cathode ray tube funnel.
The method of the present invention may also include any or all of the following steps: saturating the sponge with the carbon coating; supplying the carbon coating to the sponge through tubing in the shaft; and pumping the carbon coating from a supply of such carbon coating through the tubing to the sponge. The method may also include aligning the cathode ray tube funnel under the shaft with a conveyor system.
As to the important composition of the shaft, the method of the present invention may include making the shaft of a composite plastic material. More preferably, the method of the present invention may include making the shaft of Garolite (e.g., a fiber epoxy laminate).